Surgical methods and instruments for implanting a joint unloading system

ABSTRACT

Positioning instruments and related methods are described for implanting an joint unloading system for treating joints. The positioning instruments and methods allow the joint unloading system to be positioned at a joint such that the desired motion will occur for the particular design of a particular joint unloading system which is to be implanted. The positioning instruments include a locating instrument for locating an anatomical feature and a target location for implantation of the joint unloading system, a verification instrument for verification of the target location, an alignment guide, a placement guide for guiding placement of a part of the joint unloading system, and positioning device for aligning portions of the joint unloading system.

CROSS REFERENCES TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. application Ser. No.12/915,606, filed Oct. 29, 2010, the entire disclosure of which isexpressly incorporated herein.

BACKGROUND

The present disclosure is directed towards positioning instruments andrelated methods for implanting a joint unloading system, and moreparticularly to tools and surgical procedures for implanting a jointunloading system.

Joint replacement is one of the most common and successful operations inmodern orthopaedic surgery. It consists of replacing painful, arthritic,worn or diseased parts of a joint with artificial surfaces shaped insuch a way as to allow joint movement. Osteoarthritis is a commondiagnosis leading to joint replacement. Such procedures are a lastresort treatment as they are highly invasive and require substantialperiods of recovery and permanently alter the joint. Total jointreplacement, also known as total joint arthroplasty, is a procedure inwhich all articular surfaces at a joint are replaced. This contrastswith hemiarthroplasty (half arthroplasty) in which only one bone'sarticular surface at a joint is replaced and unincompartmentalarthroplasty in which the articular surfaces of only one of multiplecompartments at a joint (such as the surfaces of the thigh and shinbones on just the inner side or just the outer side at the knee) arereplaced.

Arthroplasty as a general term, is an orthopaedic procedure whichsurgically alters the natural joint in some way. This includesprocedures in which the arthritic or dysfunctional joint surface isreplaced with something else, and procedures which are undertaken toreshape or realign the joint by osteotomy or some other procedure. Aswith joint replacement, these other arthroplasty procedures are alsohighly invasive procedures characterized by relatively long recoverytimes. A previously popular form of arthroplasty was interpositionalarthroplasty in which the joint was surgically altered by insertion ofsome other tissue like skin, muscle or tendon within the articular spaceto keep inflammatory surfaces apart. Another previously donearthroplasty was excisional arthroplasty in which articular surfaceswere removed leaving scar tissue to fill in the gap. Among other typesof arthroplasty are resection(al) arthroplasty, resurfacingarthroplasty, mold arthroplasty, cup arthroplasty, silicone replacementarthroplasty, and osteotomy to affect joint alignment or restore ormodify joint congruity. When successful, arthroplasty results in newjoint surfaces which serve the same function in the joint as did thesurfaces that were removed. Any chondrocytes (cells that control thecreation and maintenance of articular joint surfaces), however, areeither removed as part of the arthroplasty, or left to contend with theresulting joint anatomy. Because of this, none of the therapies whichremove the joint surfaces are chondro-protective.

A widely-applied type of osteotomy is one in which bones are surgicallycut to improve alignment. A misalignment due to injury, bone abnormalityor disease in a joint relative to the direction of load can result in animbalance of forces and pain in the affected joint. The goal ofosteotomy is to surgically re-align the bones at a joint and therebyrelieve pain by shifting forces across the joint to less damaged jointsurfaces. This can also increase the lifespan of the joint. Whenaddressing osteoarthritis in the knee joint, this procedure involvessurgical re-alignment of the joint by cutting and reattaching part ofone of the bones at the knee to change the joint alignment, and thisprocedure is often used in younger, more active or heavier patients.Most often, high tibial osteotomy (HTO) (the surgical re-alignment ofthe upper end of the shin bone (tibia) to address knee malalignment) isthe osteotomy procedure done to address osteoarthritis and it oftenresults in a decrease in pain and improved function. However, HTO doesnot address ligamentous instability—only mechanical alignment. HTO isassociated with good early results, but results deteriorate over time.

It has been found that excess loading of the joint is the primarycontributing factor in the progression of osteoarthritis disease. It hasalso been shown that a decrease in load, such as by weight loss canresult in decrease in disease progression and in pain relief.

Certain approaches to treating osteoarthritis contemplate externaldevices such as braces or fixators which attempt to control the motionof the bones at a joint or apply cross-loads at a joint to shift loadfrom one side of the joint to the other. A number of these approacheshave had some success in alleviating pain by reducing loads on diseasedjoints but have ultimately been unsuccessful due to lack of patientcompliance or the inability of the devices to facilitate and support thenatural motion and function of the diseased joint.

Certain prior approaches to treating osteoarthritis have also failed toaccount for all of the basic functions of the various structures of ajoint in combination with its unique movement. In addition to addressingthe loads and motions at a joint, an ultimately successful approachshould both acknowledge the dampening and energy absorption functions ofthe anatomy, and be implantable via a minimally invasive technique.Device constructs which are relatively rigid do not allow substantialenergy storage. For these relatively rigid constructs, energy istransferred rather than stored or absorbed relative to a joint. Bycontrast, the natural joint is a construct comprised of elements ofdifferent compliance characteristics such as bone, cartilage, synovialfluid, muscles, tendons, ligaments, etc. as described above. Thesedynamic elements include relatively compliant ones (ligaments, tendons,fluid, cartilage) which allow for substantial energy absorption andstorage, and relatively stiffer ones (bone) that allow for efficientenergy transfer. The cartilage in a joint compresses under applied forceand the resultant force displacement product represents the energyabsorbed by cartilage. The fluid content of cartilage also acts tostiffen its response to load applied quickly and dampen its response toloads applied slowly. In this way, cartilage acts to absorb and store,as well as to dissipate energy.

Approaches for surgically implanting extra-articular mechanical jointunloading apparatus or joint unloading systems have been developed. Asprecise and effective placement are important to the efficacy of animplanted extra-articular mechanical unloading apparatus, furtheradvancements in patient preparation and device-to-anatomy juxapositionalrelationships have been found to be both useful and necessary.

With the foregoing applications in mind, it has been found to benecessary to develop effective systems and tools for mountingimplantable joint unloading system to body anatomy.

For joint unloading systems to function optimally, they must be selectedand positioned to unload the joint without overloading the implant.Therefore, what is needed is a refined surgical approach to implanting adevice which complements underlying or adjacent anatomy. The presentdisclosure satisfies these and other needs.

SUMMARY OF THE DISCLOSURE

Briefly and in general terms, the present disclosure is directed towardstreating diseased or mal-aligned body joints, typically affected byosteoarthritis, using a joint unloading system without limiting therange of motion of the patient's articulating joint. The positioninginstruments and related methods are described herein for implanting suchjoint unloading system.

In one embodiment, a method of implanting a device at a joint includesthe steps of inserting a first reference marker into a first bone of thejoint, inserting a second reference marker into a second bone of thejoint, connecting the first and second reference markers to averification tool, moving the joint through a predetermined range ofmotion and utilizing the verification tool to determine whether thefirst and second reference markers move in a desired kinematic patternwith respect to one another throughout the predetermined range ofmotion, relocating one of the reference markers if the desired kinematicpattern is not achieved, and implanting the device across the joint.

In another embodiment, a verification tool for verification of alocation for implantation of an extra-articular joint unloading deviceat a joint includes a tool body, a first connection member on the toolbody, the first connection member configured to be connected to a firstreference marker located in a first bone, the first connection memberallowing rotation of the tool with respect to the first bone, a secondconnection member on the tool body, the second connection memberconfigured to be connected to a second reference marker located in asecond bone, the second connection member allowing rotation of the toolwith respect to the second bone, wherein at least one of the first andsecond connection members is movable with respect to the tool body, andan indicator configured to provide a user with information about thelocation of at least one of the first and second reference markers asthe joint is articulated.

In another embodiment, the verification tool can include a first snap-onconnection to a first reference marker located on a first bone and asecond snap-on connection to a second reference marker on a second bone.The tool further includes a handle having indicators for reflectingkinematic patterns of the reference markers as the joint is articulated.The handle is configured to extend out and away from an interventionalsite for convenient manipulation and reading of the indicators by anoperator.

In one embodiment, an alignment guide for placing an joint unloadingdevice at a joint includes a body configured to receive a plurality ofreference markers inserted into bones on either side of a knee joint andan indicator rod extending longitudinally from the body, wherein theindicator rod is configured to be aligned with an axis of the tibia whenthe knee joint is placed in extension.

In another embodiment, a tool for selecting one base from among aplurality of bases having different base geometries for an implant at ajoint includes, a tool body having a bone contacting surface shapegenerally corresponding to a bone contacting surface shape of theplurality of bases from which the one base is to be selected, a pointerrotatably connected to the trial base, an indicia and indicator armportion rotatably connected to the trial base. When the trial base ispositioned on a bone of the joint, the pointer is disposed in a positionrelative to the indicia that indicates a desired base contour to beselected.

In another embodiment of a selection tool, a femoral trial assembly caninclude a trial base which is rotatably connected to a pointer and anindicia and indication arm structure. The trial base is configured to beplaced onto the femur and the indicator arm is alignable with a tibialreference marker. When so configured, the pointer identifies from theindicia the best angular contour for the femoral base. Various angles ofcontours are contemplated for the femoral base.

In a further embodiment, a system for selecting one base from among aplurality of bases having different base geometries for an implantablejoint unloading system comprises an alignment guide comprising a bodyhaving at least one opening for receiving a first reference markerinserted into a femur and at least one opening for inserting a secondreference marker into a tibia, and an indicator rod extending from thebody, wherein the indicator rod is configured to be aligned with an axisof tibia when the knee joint is placed in extension; and a trial basehaving at least one opening configured to be received over the firstreference marker, a pointer movably connected to the trial base, and anindicia and indicator arm portion rotatably connected to the trial base,wherein, when the trial base is positioned on a bone of the joint, thepointer is disposed in a position relative to the indicia that indicatesa desired base to be selected.

In another embodiment, a method for selecting one base from among aplurality of bases having different base geometries for an implantablejoint unloading system comprises the steps of inserting a firstreference marker in the femur; connecting an alignment guide to thefirst reference marker with an indicator rod extending from thealignment guide aligned with an axis of tibia when the knee joint isplaced in extension; inserting a second reference marker through anopening in the alignment guide and into the tibia; and positioning atrial base over the first reference marker, rotating the trial baseuntil an arm of the trial base points to the second reference marker,and selecting a desired base to be implanted based on an indicia shownon the trial base.

Other features of the joint unloading system, instruments and methodswill become apparent from the following detailed description, taken inconjunction with the accompanying drawings, which illustrate, by way ofexample, the principles of the embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view, depicting an extra-articular implantablemechanical joint unloading system;

FIG. 2 is a side view, depicting the absorber of the system of FIG. 1with the sheath removed;

FIG. 3 is a side view, of a position verification tool for location of acorrect position for the joint unloading system of FIG. 1;

FIG. 4 is a perspective view, of the verification tool of FIG. 3 in useon a patient;

FIG. 5 is a perspective view, of the verification tool of FIG. 3;

FIG. 6A is a perspective view, of alternative approach to a verificationtool;

FIG. 6B is a cross-sectional view, depicting the verification tool ofFIG. 6A;

FIG. 6C is a top view, depicting the verification tool of FIG. 6A;

FIG. 7A is a perspective view of a bullseye tool for inserting areference marker into a bone at a desired location;

FIG. 7B is a top view of a portion of the bullseye tool of FIG. 7A;

FIG. 7C is a side view of an alternative embodiment of a bullseye tool;

FIG. 7D is an exploded perspective view of the bullseye tool of FIG. 7C;

FIGS. 8A-8C are perspective and side views of an alignment guideassembly;

FIG. 8D is a side view, depicting the alignment guide assembly of FIGS.8A-C in use;

FIG. 8E is a perspective view, depicting forming a tunnel betweenincision sites;

FIG. 9A is a top perspective view of a placement guide used tofacilitate correct positioning of the base;

FIG. 9B is a side perspective view of the placement guide of FIG. 9A;

FIG. 10 is a top view of the placement guide of FIG. 9A temporarilyattached to a base;

FIG. 11 is a perspective view of the placement guide and base as theyare positioned for attachment of the base to a bone of a patient;

FIG. 12 is a perspective view of the base attached to the bone of apatient with the placement guide removed;

FIG. 13A is a side perspective view of an absorber positioning collar;

FIG. 13B is a bottom perspective view of the absorber positioning collarof FIG. 11A;

FIG. 14 is a top view of the positioning collar of FIG. 13A positionedbetween a base and absorber;

FIGS. 15A-15C are perspective, top and side views of a femoral trialaccording to an aspect of the present disclosure;

FIGS. 16A-16C are perspective, front and back views of an alternativeapproach to a femoral trial base;

FIG. 16D is a side view, depicting use of the femoral trial base ofFIGS. 16A-C;

FIGS. 17A-17B are top and perspective views of a base for forming partof a system for placing an joint unloading device at a joint accordingto an aspect of the present disclosure;

FIGS. 18A-18B are top and perspective views of a placement guide forforming part of a system for placing an joint unloading device at ajoint according to an aspect of the present disclosure;

FIG. 19 is a side view of a locking pin forming part of a system forplacing an joint unloading device at a joint according to an aspect ofthe present disclosure; and

FIGS. 20A-20B are perspective and top views of a system for placing anjoint unloading device at a joint according to an aspect of the presentdisclosure.

DETAILED DESCRIPTION

Referring now to the drawings, which are provided by way of example andnot limitation, the present disclosure is directed towards apparatus fortreating body tissues. In applications relating to the treatment of bodyjoints, the described approach seeks to alleviate pain associated withthe function of diseased or malaligned members forming a body joint.Whereas the present invention is particularly suited to address issuesassociated with osteoarthritis, the energy manipulation accomplished bythe present invention lends itself well to broader applications.Moreover, the present invention is particularly suited to treatingsynovial joints such as the knee, finger, wrist, ankle and shoulder.

In one particular aspect, the presently disclosed joint unloadingsystems involve varying energy absorption and transfer during therotation of a joint, such as a knee joint. FIG. 1 illustrates animplantable joint unloading system for absorption of forces normallytransmitted through a joint in order to relieve pain, such as painassociated with osteoarthritis.

U.S. Patent Publication No. 2009/0014016, which is incorporated hereinby reference in its entirety, describes certain embodiments ofextra-articular energy absorbing systems. These energy absorbing systemsinclude geometry which accomplishes variable energy absorption designedto minimize and complement the dampening effect and energy absorptionprovided by the anatomy of the body, such as that found at a body joint.It has been postulated that to minimize pain, in an osteoarthritic jointabsorption of 1-40% of forces, in varying degrees, may be necessary.Variable absorption in the range of 5-20% can be a target for certainapplications. In certain specific applications, temporary distraction(e.g., less than 3 months) is employed in the energy manipulationapproach.

Referring now to FIG. 1, one embodiment of an joint unloading system 50is shown affixed to a knee joint to absorb at least a portion of theenergy normally transmitted by the knee anatomy. The joint unloadingsystem 50 includes a proximal 52 base positioned on the femur 56 and adistal 54 base positioned on the tibia 58 of the typical knee joint. Itis noted that portions of the base 52, 54 are contoured to matchpotential mounting surfaces of the femur and tibia 56, 58. Also shown isan energy absorbing or joint unloading device 60 that is located betweenand mounted to the bases 52, 54. In FIG. 1A, the joint unloading system60 is shown with a sheath 61 which covers internal components, protectsthe moving elements from impingement by surrounding tissues and preventsthe devices from damaging surrounding tissue. For viewing purposes thesheath 61 is omitted from FIG. 2.

The joint unloading system 50 as shown includes two springs 62, 64,however other numbers of springs may also be used. The joint unloadingsystem 50 has the capacity to absorb energy in addition to transferringenergy from the joint. FIG. 1 shows the knee joint at full extension. Inthe example of FIG. 1, maximum load is applied to the springs 62, 64 ofthe joint unloading device 50 at full extension during the stance phaseof the gait cycle. When the knee joint is flexed to 90°, such as duringthe swing phase of the gait cycle or when the patient is seated, zeroload is absorbed from the knee by the springs 62, 64. In this example,when the joint unloading device 50 is correctly positioned on the knee,the device is actively working in compression when the knee is at ornear full extension. The joint unloading device 50 lengthens as the kneeswings from full extension to flexion and subsequently shortens as theknee swings from flexion to full extension such that the springs beginto be compressed between the ends of the device to absorb at least aportion of the load that the knee articulating surfaces normally wouldexperience.

The joint unloading device 50 and bases 52, 54 are mounted across thejoint such that once the spring has achieved a predetermined amount ofcompression, and therefore load, the articulating surfaces of the kneethen carry a portion of the load in combination with the joint unloadingdevice such that the joint unloading device does not “bottom out”.

Still referring to FIG. 1, as well as FIG. 2, one embodiment of an jointunloading device 60 includes two machined springs 62, 64. These springs62, 64 are each positioned about guides (not shown) which support thesprings allowing the springs to act in compression when the knee is inextension or at low flexion angles and support the springs in anunloaded position when the knee is at higher flexion angles. The guidesabout which the springs 62, 64 are located may be in the form oftelescoping members, such as a piston and barrel which allow theopposite ends of the joint unloading device 60 to move in a linear pathtoward and away from each other. The joint unloading device alsoincludes a proximal (femoral) end 66 and a distal (tibial) end 68 whichare connectable to the bases 52, 54 by a known connection mechanism 70,such as a taper lock.

The joint unloading device 60, as illustrated, also includes two balland socket joints within the proximal and distal ends 66, 68 which allowanterior/posterior, medial/lateral, and axial rotation of the jointunloading device 60 with respect to the bases 52, 54. The range ofmotion of the components of the system can be determined by thebearing/socket geometry, base/absorber geometry and relative position ofthe base to absorber at final implantation. Identical ball/socketsarrangements can be provided on both sides of a knee joint but differentarrangements are also contemplated. The absorber springs 62, 64 act toabsorb load from the medial compartment of the knee while thearticulation of the ball/sockets and the telescoping of pistonassemblies of the absorber allow the device to accommodate full kneerange of motion.

For best performance of the joint unloading system 50, the femoral base52 and the associated ball and socket articulating surfaces at thefemoral end 66 of the joint unloading device 60 should be preciselypositioned. In order to more easily locate the accurate position forthis proximal base 52 and articulation a position verification tool andrelated method have been developed.

Conventional or surgical or minimally invasive approaches are taken togain access to a body joint or other anatomy requiring attention.Arthroscopic approaches are contemplated when reasonable to both implantthe energy manipulation assembly as well as to accomplish adjusting animplanted assembly.

In one approach for treating a knee, an implantable extra-articularenergy absorber system is designed to reduce medial compartment loads ofthe knee. The absorber system is comprised of two contoured basecomponents, a kinematic load absorber and a set of bone screws. Theimplanted system is both extra articular and extra capsular and residesin the subcutaneous tissue on the medial aspect of the knee. The deviceis inserted through two small incisions superior to the medial femoralcondyle and inferior to the tibial plateau. The contoured basecomponents are fixed to the medial cortices of the femur and tibia usingbone screws.

An energy absorber 60 having a spring value of about twenty pounds canprovide therapeutic benefit for patients of 300 pounds or less. Higherspring forces would provide greater reduction in joint load and maycorrelate to greater symptom (i.e., pain) relief.

It has been found that a medial compartment of a knee of an averageperson with osteoarthritis can benefit from an absorber set forcompression between 1 mm and 10 mm, and preferably 3-6 mm with a springor absorber element that accommodates a range from 20-60 pounds. In onepreferred embodiment, the absorber is set for about 4 mm of suchcompression and a pre-determined load of about 40 pounds. An absorber of40 pounds load absorption can unload the medial compartment of apatient's knee from 25-40 pounds.

The femoral and tibial base components can be contoured to ensureoptimal fit to the bony surfaces and can be plasma sprayed coated withporous titanium and/or coated with hydroxyapatite on bone contactingsurfaces to promote bony ingrowth and enhance osteointegration.

The position verification tool 100 shown in FIGS. 3-5 is used duringsurgery to verify a position of the femoral base 52 and the femoralarticulation surface of the absorber 60 to achieve the most functionalposition of the system 50. The preferred implantation position of thesystem 50 is achieved when the springs 62, 64 are in a compressedorientation during the swing phase of the gait including full extensionand low flexion angles of the knee joint. The springs are in a lesscompressed or in an uncompressed position at 45 degrees of flexion ofthe knee, and by 90 degrees flexion of the knee the springs arepreferably uncompressed or nearly uncompressed. This configurationcorresponds to the composition of the gait cycle where the largestforces are exerted on the knee joint near full extension and theseforces are greatly decreased when the knee is flexed during the swingphase of the gait.

The position verification tool 100 as described herein verifies that thedesired motion will occur for the particular design of a particularjoint unloading system which is to be implanted. Although the positionverification tool 100 has been described for use with the jointunloading system 50, it should be understood that the verification toolcan also be used to verify fixation positions of other implantablesystems are designed to have a particular desired kinematic pattern as ajoint moves through a particular range of motion.

The position verification tool 100 is used in a method of implanting thejoint unloading system 50 by inserting first and second referencemarkers into first and second bones on opposite sides of the joint andconnecting the first and second reference markers to the verificationtool. The verification tool 100 then is used to determine whether thefirst and second reference markers move in a desired kinematic patternwith respect to one another. Examples of kinematic patterns include 1)reference markers moving away from each other as the joint moves fromextension to flexion; 2) reference markers staying within a certaindefined distance of each other as the joint moves from extension toflexion; 3) reference markers moving toward each other as the jointmoves from extension to flexion; and 4) reference markers moving awayfrom each other and then toward each other as the joint moves.

In addition to verification of the position for placing one or more ofthe bases 52, 54, the position verification tool 100 can also be used toselect an joint unloading member 60 when different sizes orconfigurations of joint unloading members are available, such as thoseas described in U. S. Patent Publication No. 2009/0014016.

The position verification tool 100 includes a body 102 having a firstend 110 for attachment to reference markers in the patient and a secondgauge end 112 which extends at an angle from the first end formonitoring relative motion of the reference markers and the bones. Thefirst end 102 of the tool 100 has a first connection point 104 with afixed longitudinal location on the body. The first connection point 104may include a guide hole and a guide ball which allows a marker to pivotwithin the tool body 102 but does not allow the first connection pointto translate. The first connection point may also include an offset 105,shown in FIG. 5, which causes the tool to sit off the bone by a distanceof the offset allowing the tool to rotate more easily withoutinterference from the bone. The tool 100 has a second connection point106 with a longitudinally movable location. The second connection point106 may also include a guide hole through a guide ball which allows amarker to pivot within the tool body 102. The guide ball at the secondconnection point 106 may also include an offset 105. The guide ballsallow the tool 100 to rotate about the first and second referencemarkers or K-wires throughout the range of motion of the joint even whenthe reference markers are not exactly parallel.

The second connection point 106 is secured to a flexible ribbon 108which is longitudinally movable on the tool 100. The flexible ribbon 108acts as a gauge to monitor the relative motion of the reference markerswhile moving the joint through a predetermined range of motion. Thus,the second connection point 106 moves longitudinally on the verificationtool 100 as the joint is moved through a range of motion. Theverification tool 100 is used to determine whether the first and secondreference markers move in a desired kinematic pattern with respect toone another throughout the predetermined range of motion. As discussedabove, the desired kinematic pattern may be a pattern where thereference markers move apart as the joint moves from extension toflexion. If the desired kinematic pattern is not achieved, one of thereference markers is relocated. The verification tool may then be usedto check the new position.

Other configurations of the verification tool 100 are also contemplatedin which the motion between the first and second connection points 104,106 is accommodated and verified in other manners. For example, atelescoping verification tool 100 may be used including bars oridentifying bands on a portion of the telescoping parts.

In an alternative approach, as shown in FIGS. 6A-C, a kinematicverification tool 110 can be embodied in an elongate device. The tool110 includes a femoral side assembly 112 and a tibial side assembly 114.As best seen in FIG. 6B, the femoral side assembly 112 includes aninternal bore sized and shaped to receive a length of the tibial sideassembly 114. The femoral side assembly 112 is generally straight andthe tibial side assembly includes a curved or flexible mid-section. Itis to be appreciated that the femoral and tibial side assemblies 112,114 are rotatable and longitudinally translatable with respect to eachother. They each further include enlarged sections 115 including slots116 for receiving K-wires or other referencing structure projecting fromthe femur and tibia, respectively. The enlarged section 115 of the tibiaside assembly 114 can include two such slots 116 for receivingreferencing structure. Such slots are configured to provide convenientsnap-on connections with referencing structure, in that referencingstructure can be snapped into the enlarged section 115 by moving thetool 110 laterally with respect thereto.

The kinematic verification tool 110 further includes a handle insert 118configured within a bore extending through the tibial side assembly 114.Again, as best seen in FIG. 6B, a screw 120 is contained within thehandle insert 118. The screw 120 is connected to a wire 122, such as aNitinol wire, that extends through the verification tool 110 to thefemoral side assembly 112. This connection between the handle insert118, screw 120 and wire 122 allows the tool 110 to track the relativemotion of the femoral and tibial assemblies. The handle insertadditionally includes indicators 124, 125 which facilitate observing thekinematic pattern of the tibial and femoral reference markers on whichthe tool 110 has been secured. Where the tibial and femoral referencemarkers moving away from each other this motion will be reflected aspositive movement in the indicators 124. Where the tibial and femoralreference markers move toward one another during motion of the joint theindicators 125 indicate a negative motion.

In one approach to a surgical method, an initial step in treatmentinvolves identifying a patient's Blumensaat's line, which is aradiographic and structural feature of a femur. Using Blumensaat's lineas an anatomical radiographic landmark, an acceptable region and targetarea can be identified for placement of a center of rotation of afemoral socket just anterior and/or proximal of the center of rotationof the femur. As shown in FIG. 4, a reference marker 104 or K-wire ispositioned in the femur under fluoroscopy or another imaging technique.The placement of the femoral reference marker 104 can be done manuallywithout the assistance of a placement tool. Alternatively, a bullseyetool guide 200 or other placement tool may be used to insert thereference marker 104 at a desired target area.

The bullseye tool 200 shown in FIGS. 7A and 7B is employed as a guidethrough which a K-wire 130 is inserted into the femur either through thepatient's skin or after making a small incision. It is to be noted thatanatomical and/or radiographic landmarks (e.g., center of Blumensaat'sline, inferior and posterior regions of the femoral condyles) can aid inmanually positioning a K-wire in the target region or location, with orwithout the bullseye instrument. The bullseye tool is used for locatinga center of rotation of the femoral socket by locating an anatomicalreference location, such as the center of Blumensaat's line, andlocating the center of rotation of the implant a predetermined distanceand direction from the anatomical reference location.

When using the bullseye tool 200, the bullseye tool is placed with acenter pin 202 of the bullseye tool on the midpoint of Blumensaat'sline. The tool is rotated until two wings 204 of the tool (withradiopaque markers) are parallel to Blumensaat's line. Vertically spacedapart radiopaque rings 206 are arranged in the center portion of thebullseye tool 200 and when these rings are aligned (concentric) in a thebullseye tool is perpendicular to the fluoroscopic view and properlyaligned to insert a reference marker 130 perpendicular to the lateralview. In this position, the K-wire or reference marker 130 is placedthrough a hole 208 in the tool 200 to locate the center of rotation ofthe femoral socket of the joint unloading device 60. The hole 208, ashown, has a trajectory which is parallel to the direction of imagingwhen the concentric rings are aligned. However, other trajectories ofthe reference marker 130 may be achieved by varying the trajectory ofthe hole in the bullseye tool 200.

The location of the hole 208 in the bullseye tool 200 is designed to bejust anterior and proximal of the midpoint of Blumensaat's line when thetool is positioned as described above. Since it has been shown that themidpoint of Blumensaat's line is a good radiographic approximation of acenter of rotation of the femur, the location of the reference marker130 anterior and proximal of this midpoint of Blumensaat's line has beenshown to be a starting point for finding a location of the center ofrotation of the femoral articulation and achieving a desired kinematicpattern where the reference markers move apart as the joint moves fromextension to flexion.

FIGS. 7C and 7D show an alternative embodiment of a bullseye tool 220having a handle 222 and a separable tip 226. The bullseye tool 220 has alumen 232 for receiving a K-wire or other reference marker and a ringshaped radiopaque marker 228 concentrically surrounding the centrallumen 232. A pin 224 is provided on the tip 226 for holding the tip ofthe bullseye tool in place while the reference marker is inserted intothe bone. The tip 226 can be snapped out of the handle 222 for disposalin a sharps container by pressing on a button 234 formed by the uppersurface of the tip 226.

Next, with reference to FIGS. 8A-E, an alignment guide 250 can beemployed to facilitate aligning a femoral trial and an absorber, as wellas to properly position the absorber while securing a tibial base. Thealignment guide 250 has a generally rectangular shaped body 252.Extending substantially perpendicular to a long dimension of the body252 are a plurality of tubes 254, 256, 258 for inserting referencemarkers or K-wires into the bones of a joint to position these referencemarkers at desired relative positions. A first tube 254 is sized andshaped to receive the femoral reference marker 130. The second and thirdtubes 256, 258 are configured to receive reference markers (i.e. item132) extending from the tibia. The reference markers are generally inthe form of K-wires which may be provided in differing lengths. Anindicator rod 260 is further provided on the alignment guide 250 and isconfigured to extend longitudinally from an end of the body 252 nearestthe second and third tubes 256, 258. As shown in FIG. 8A either thesecond or third tube 256, 258 may include an angled tip which functionsto penetrate the bone slightly to maintain the alignment guide 250 inposition while reference markers are driven into the bone.

In use, the patient's leg is straightened and a confirmation is made toensure that the knee is extended. The placement guide 250 is then placedsuch that the first tube 254 is positioned in a femoral incision andabout the femoral reference marker 130 which has been positioned asdescribed above. The body 252 of the placement guide is designed toreside outside of the tissue of the patient while the tubes 254, 256,258 extend into the surgical site. The indicator rod 260 is aligned sothat it is parallel to the tibia axis (See FIG. 8D) under fluoroscopy.An incision is then made between the second and third tubes 256, 258 toprovide access to the tibia. It is contemplated that the incision lengthis 5-8 cm. Next, a tissue tunnel is created using blunt dissectionbetween the two incisions sites (See FIG. 8E). The tunnel width isformed so as to accommodate an absorber.

With the knee in an extended position, confirmation is again made thatthe indicator rod 260 remains parallel to the tibial axis. A firsttibial reference marker 132 can be inserted into the second tube 256 ofthe alignment guide 250. The second tibial reference marker 133 is thenplaced through the third tube 258. It is to be recognized that thelocation of the tibial ball of an absorber will be at the third tibialreference 133. The first and second tibial reference markers 132, 133will assist in the femoral base selection and alignment. In addition,the tibial reference markers 132, 133 can be employed to support theabsorber prior to tibial base fixation.

As shown in FIG. 4, the verification tool 100 is inserted through atissue tunnel between first and second incisions in the leg on oppositesides of the knee joint. The tool is placed onto the first referencemarker 130 positioned in the femur and a second substantially parallelreference marker 132 is placed through the connection point 106 of thetool into the tibia. The distance between the first connection point 104and the second connection point 106 on the verification tool 100 isselected to provide the desired spacing for mounting bases to the bonesto accommodate the joint unloading member 60. Although the verificationtool 100 has been described as operating partly beneath the patient'sskin within a tissue tunnel, it should be understood that in some casesthe verification tool may be entirely underneath or entirely outside ofthe patient's skin.

The verification tool 100 includes one or more bars, bands, grids orother markings, such as the 45° and 90° bars 120 shown in FIG. 3 as wellas a pointer 122. The 45° bar shows the range of acceptable locations ofthe pointer 122 when the joint is at 45° of flexion, while the 90° barshows the range of acceptable locations of the pointer when the joint isat 90° of flexion. The bars are merely shown by way of example as one ormore other bars may also be used. The bars are merely a simplified wayof determining if there is not enough or too much space between thereference markers as the joint is articulated. If there is not enough ortoo much spacing between the reference markers, this in an indicationthat one or both of the reference markers should be moved to achieve thebest function of the joint unloading device 50.

In one embodiment of the invention, the location of the femoralreference marker is verified by placing the verification tool on thefemoral reference marker 130 as shown in FIG. 4 and inserting the tibialreference marker 132 through the connection point 106. When placing thetibial reference marker 132, the pointer 122 should be pointing at thezero mark 126. To simulate stance or loaded extension, the knee shouldbe located in extension and any medial laxity in the joint should beremoved by pulling the tibia medially to close the medial joint spaceduring placement of the tibial reference marker 132. In the event thatthe knee joint was not in full extension or the medial joint space waspartially open during placement of the tibial reference marker, theverification tool 100 can be readjusted to the zero mark 126 aftercorrecting the knee position. To verify the femoral reference markerlocation, the knee is flexed through a range of motion while thelocation of the pointer 122 with reference to the bars 120 on theverification tool 100 is observed. For example, when the knee is movedfrom extension through 45° of flexion with the medial joint space closedthe pointer position should be within the 45° bar. In addition, when theknee is moved from extension through 90° of flexion with varus, valgus,internal and external rotations, the pointer position should be withinthe 90° bar. If this verification is successful, the verification tool100 can be removed and the femoral reference marker 104 is confirmed tobe at the desired location for the center of rotation of the femoralarticulation 66. If the pointer moved outside of the bars during theprescribed motion, the femoral reference marker location should beadjusted as described below. This verification is performed under directvisualization.

The following guidelines can be used to move the femoral referencemarker 130 if the criterion of the verification tool 100 are not met. Ifthe pointer never enters either the 45° or 90° bar during theverification steps or if the pointer travels outside the bounds ofeither of the 45° or 90° bars during the specified flexion angles, a newreference marker should be inserted at a location displaced a shortdistance from the original reference marker 130. In the case of thepointer never entering either the 45° or 90° bar during the verificationsteps, the new reference marker should be inserted in a region which isdistal and/or anterior to the original marker a distance of about 1-2mm. If the pointer travels outside the bounds of either of the 45° or90° bars (moves completely past the bars) during the verification steps,a new reference marker should be inserted in a region which is posteriorto the original marker. The original femoral reference marker 130 isthen removed and the verification step is repeated with the newrelocated reference marker. The tibial reference marker 106 does notneed to be moved as the verification tool 100 can be readjusted to thezero position after the new femoral reference marker 104 is inserted.

In the event that multiple joint unloading devices 50 are available,i.e. different sizes, the verification tool may include additionalmarkings or may come in different sizes.

Although the verification tool 100 has been illustrated as using thevisual analog reference of the pointer 122 and the bars 120, it shouldbe understood that other methods may alternatively or additionally beused for verification feedback. For example, the verification tool 100can include visual, auditory, tactile, and/or digital feedback.Moreover, the verification tool 110 depicted in FIGS. 6A-C canalternatively be employed to assess the kinematic pattern of thereference markers and provide verification feedback. The verificationtool 110 of FIGS. 6A-C has the advantages of having a simpler connectionvia a snap on connection to the reference markers and easierinterpretation with a longer and flexible location for the indicia.

Once an acceptable position of the reference marker 130 is verified thejoint unloading device 50 is implanted across the joint by locating thebases 52, 54 on the bones employing the instruments and methods whichwill be described below. Particularly, the femoral base 52 is located ata preferred location with respect to the location of the referencemarker 130 to locate the center of rotation of the femoral articulation66 at the location of the reference marker.

To assist in location of the femoral base 152, a femoral placement guide300 shown in FIGS. 9A, 9B and 10 is temporarily attached to the femoralbase 152. To ensure that the femoral base 152 stays at a correctlocation during attachment to the bone, the femoral placement guide 300is configured to temporarily attach to the base and later be removedafter attachment is complete. The placement guide 300 is attached to aselected femoral base 152 by a guide knob 312 (FIG. 10) which fits intothe large distal hole 314 of the guide 300 and threads into a bone screwhole 330 of the base. The placement guide 300 includes a proximal guidehole 310 into which a K-wire or other elongated member can be insertedfor positioning. The placement guide also includes a hole 316 with anoffset 318 for receiving the reference 130 which was placed in theprevious steps. The configuration of the hole 316 and offset 318 isdesigned to locate the femoral base 152 at a position where when theabsorber 60 is attached to the femoral base, the absorber femoralarticulation 66 will be located to achieve the desired kinematics.Specifically, the location of the hole 316 with respect to the base 152corresponds to the location of the femoral articulation 66 with respectto the base when the absorber 60 is attached to the base. Additionally,the offset 318 corresponds to a desired offset of the absorber femoralarticulation 66 from the bone. A height of the offset 318 is preferablyat least 2 mm to provide sufficient clearance between the ball andsocket articulation of the absorber and the bone when the absorber isconnected to the base.

As shown in FIG. 11, the femoral base 52 with the attached placementguide 300 are placed onto the femur by sliding the placement guide hole316 over the previously placed reference marker 130. A proper positionof the femoral base 52 can be determined by placing a guide wire intothe guide wire hole 310 of the placement guide 300. The guide wireshould extend generally perpendicular to the tibial plateau andgenerally parallel to the medial femoral condyle. The femoral base 52 isheld in place by inserting one or more, and preferably two or more,K-wires 322 through the available K-wire holes 320 in the femoral base.These K-wires 322 will hold the femoral base 52 in place duringplacement of the bone screws 332 through the bone screw holes 330. Thebone screws may include combinations of unicortical cancellouscompression screws, locking screws, and bicortical compression screws.The screws may be placed before or after removal of the placement guide300 from the base 52. Preferably, the placement guide is removable fromthe base 52 by removing the guide knob 312 after the base is secured tothe bone by bone screws. FIG. 12 illustrates the placement of thefemoral base 52 after the placement guide 300 has been removed. Once thefemoral base 52 is secured to the bone, the base is ready for attachmentof the absorber 60 and securing of the tibial base 54.

The femoral base 52 can be provided in different shapes and/or sizes aswell as versions for left and right knees. The femoral placement guide300 can be provided in versions which coordinate with the differentbases. In addition, in the event that different absorber configurationsare available, the placement guide 300 can be provided in differentversions to accommodate the absorbers.

In addition to or as an alternative to the femoral placement guide 300,trial bases can be used to located a desired orientation and position ofthe femoral base 52. For example, a trial base in the form of a onepiece member having a shape of the combination of the base and placementguide shown in FIG. 10 can be used to determine and mark a position forthe placement of the base. In the case of a trial base, the trial caninclude the offset to determine correct spacing of the articulation fromthe bone and can include the guide wire hole to aid in determiningangular position with respect to the joint surfaces.

In one embodiment, once the femoral base 52 has been secured to the bonethe absorber 60 with the attached tibial base 54 is inserted through atissue tunnel between the skin and bone of the patient and the socket 66of the absorber is connected to the femoral base 52. Methods andinstruments for connecting the absorber sockets 66, 68 to the bases 52,54 are shown and described in further detail in US Patent PublicationNo. 2009/0014016. Such connection of the sockets to the bases may be bytaper locks, locking pins, locking screws and the like. Once theabsorber 60 has been connected to the femoral base 52, the system isready for attachment of the tibial base 54 to the tibia of the patient.

To assist in proper alignment and positioning of the absorber 60 andpositioning of the tibial base 54, an absorber positioning collar 400 isshown in FIGS. 13A and 13B. Setting the trajectory of the femoralbearing 66 is important to achieve desired motion of the absorberrelative to the motions of the knee and the implantable system. If thebearing resides in an inappropriate plane then one of the ball/socketscan have insufficient motion in at least one direction. The absorberpositioning collar 400 includes a handle 410, a femoral base receivingrecess 412, and a femoral socket receiving recess 414. The positioningcollar 400 also includes an optional K-wire hole 420 for temporarilysecuring the positioning collar in place. The absorber positioningcollar 400 is designed to be temporarily located between the femoralbase 54 and the femoral socket 66 to aid in positioning. The collar 400sets the absorber position relative to the implanted base 52. Sinceanatomies vary, the collar 400 may be configured to fix the absorberposition or to allow some limited range of angles of the absorber withrespect to the base. For example, where a total range of motion of thearticulation is greater than 100 degrees, the motion may be limited bythe collar 400 for purposes of initial positioning to less than 45degrees, and preferably about 20 degrees or less.

In addition to setting the absorber angular position, the collar 400 caninclude one or more features for setting a desired range of offsetdistances between the absorber and the underlying bone.

As shown in FIG. 14, the absorber positioning collar 400 is placed ontothe femoral socket 66 of the absorber 60 with the recesses 412, 414receiving the distal end of the femoral base and the femoral socket,respectively. The positioning collar 400 temporarily limits motion ofthe femoral socket to a reduced range of motion which corresponds toacceptable positions of the absorber at full extension. When the knee isplaced in full extension and the medio-lateral laxity of the joint isremoved by applying varus stress on the knee, the absorber is in aproper position. The tibial base 54 can then be fixed to theanteriomedial surface of the tibia by initially stabilizing with K-wiresfollowed by screw fixation in a manner similar to that used to securethe femoral base 52. In one embodiment, an additional temporary tibialcollar may also be used to limit the available range of motion of thetibial articulation during implantation.

The terms “spring” and “absorber” are used throughout the descriptionbut these terms are contemplated to include other energy absorbing andcompliant structures to accomplish the functions of the invention asdescribed in more detail herein.

While screws are used to fix the femoral and tibial bases 52, 54 to thebone, those skilled in the art will appreciate that any fasteningmembers known or developed in the art may be used to accomplish desiredaffixation. Although the bases 52, 54 depicted include four to fiveopenings and screws, it is contemplated that other embodiments of thebases may have any number of openings for screws.

FIGS. 15A-15C show a femoral trial 500 according to an aspect of thepresent disclosure. The femoral trial 500 functions as a tool forselecting one base from among a plurality of bases having different basegeometries for an implant at a joint, such as when the femoral base isprovided in two or more versions to accommodate different patientanatomies, such as the 40°, 45°, and 50° base shapes disclosed in U.S.patent application Ser. No. 12/755,335, which is incorporated byreference in its entirety. The trial 500 comprises a tool body 501having a bone contacting surface 503 with a shape generallycorresponding to the shape of bone contacting surfaces of the pluralityof bases from which the one base is to be selected. It will beappreciated that the principles associated with the femoral trial areapplicable to other joints and joint components, as well.

A bottom surface 503 of the body 501 conforms generally to the shape ofthe bone to which it is desired to attach a base. A top surface 505 ofthe body 501 that faces away from the bone may be generally flat or ofany other convenient shape for grasping and manipulating the tool.

A guide opening 507 is provided on the tool body 501 and extends throughthe tool body. The opening 507 is sized to be received over a referencemarker, such as a K-wire which has been placed into the bone. The guideopening 507 has indicia 509 adjacent to the opening and corresponding toat least some of the plurality of bases. The guide opening 507 isgenerally conical, with a wide end 511 of the cone being disposed on aside of the tool body 501 opposite the bottom surface 503 of the toolbody intended to face the bone. The indicia 509 are disposed on the toolbody 501 at the wide end 511 of the cone of the guide opening 507. Theguide opening 507 extends through the tool body 501. In the embodimentof FIGS. 15A-15C, the indecia 509 are located on projecting portions 513that include two shafts 513 a and 513 b between which the generallyconical opening extends.

During a procedure of placing an joint unloading device, the tool body501 is positioned on a bone of the joint in a desired alignment with thebone. In the case of the femoral trial 500, an elongated wire referencemarker 130 (FIG. 11) is installed in the bone so as to extend generallyperpendicular to the tibial plateau and generally parallel to the medialfemoral condyle extends through the guide opening. The tool body 501 ispositioned so that a long axis 515 (FIG. 15B) of the tool body isaligned parallel to an extended tibial axis and so that the trial basefits on the femur geometry in a fashion so that it is stable on thefemur, and the reference marker extends through the guide opening 507.

The reference marker 130 extending through the guide opening 507 willthen be disposed in a position relative to the indicia 509 thatindicates which base is to be selected from among the plurality ofbases. For example, the embodiment of FIGS. 15A-15C is intended tofacilitate selection of one of the 40°, 45°, and 50° base shapesdisclosed in U.S. patent application Ser. No. 12/755,335. In the exampleof FIG. 15B, the indicia 509 is in the form of markings that read “40°”and “50°”. If the reference marker 130 is centered in the cone of theguide opening 507 and not touching either side, then a 45° base isindicated. If the reference marker 130 touches the side of the conemarked with the “40°” indicia 509, then a 40° base is indicated. If thereference marker 130 touches the side of the cone marked with the “50°”indicia 509, then a 50° base is indicated.

With reference now to FIGS. 16A-C, an alternative femoral trial assembly550 is presented. The femoral trial assembly 550 includes a trial base552, which is rotatably connected to both a pointer 554 and an indiciaand indicator arm structure 556. As with the previous approach, thetrial base portion 552 has a bone contacting surface 557 having a shapegenerally corresponding to the shape of bone to which the base is to beattached. The indicia portion 558 of the indicator arm structure 556 caninclude angular markings such as the 40, 45 and 50 degree markingsshown, which correspond to various contours for a femoral base. Theindicator arm portion 560 is an elongate member that extends away fromthe indicia portion 558. The pointer 554 overlays the indicia portion558 and is employed to select the best contour for the femoral base. Theindicator arm structure 556 is rotatable with respect to the trial base552 by a first pivot joint. A second pivot joint 559 allows theindicator arm portion 560 and connected indicia portion 558 to pivotwith respect to the pointer 554. Together the first and second pivotjoints 555, 559 allow rotation of the indicator arm 560 in twodimensions with respect to the trial base 552 to accommodate a varietyof femur configurations. A through hole 553 through the indicator armstructure 556 is provided so that the femoral trial assembly can bereceived over the femoral reference marker 130.

In use to select a femoral base (See FIG. 16D), the periostiumoverlaying a femur can be removed or lifted so that the trial base 552of the trial base assembly 550 can contact bone. The assembly 550 ispositioned over or about a femoral reference marker 130. The indicatorarm portion 560 is then aligned with the second tibial reference marker133 and the pointer 554 will identify the correct femoral base contour,for example as 40, 45 or 50 degrees to be selected.

FIGS. 17A-17B show a base 600, FIGS. 18A-18B show a placement guide 700,FIG. 16 shows a locking pin 800 of a system 900, shown in FIGS. 20A-20B,for placing an joint unloading device at a joint, such as a knee joint.The system 900 is designed for use in placing a femoral base of an jointunloading device on a patient's femur, however, it will be appreciatedthat the principles associated with the system are applicable to otherjoints and joint components, as well. The system 900 is particularlysuited for use in connection with placement of a femoral base of thetype that is designed to be placed with an end of the base offset fromthe bone surface in order to accommodate an articulating portion of theimplant in manner disclosed in U.S. patent application Ser. No.12/755,335, which is incorporated by reference.

The base 600, shown by itself in FIGS. 17A-17B, is configured to besecured to the bone adjacent the joint and has a body 601 including aninner surface 603 facing the bone and conforming generally the shape ofthe bone, and an outer surface 605 facing away from the bone. The body601 further includes a first placement guide mounting surface 607 and afirst connector component 609.

The placement guide 700, shown by itself in FIGS. 18A-18B, can be formedof, e.g., molded plastic, and includes a second placement guide mountingsurface 701, a second connector component 703 adapted to mate with thefirst connector component 609, and an offset member 705. The placementguide 700 is attachable to the base 600 in an attached position, seen inFIGS. 20A-20B, such that the first and second placement guide mountingsurfaces 607 and 701 abut when the first and second connector components609 and 703 mate. The placement guide 700 is designed to be removablefrom the base 600 after the base has been secured to the bone so thatsocket components (not shown in FIGS. 17A-20B) can be attached to thebase. After the sockets are attached to the base, an absorber (not shownin FIGS. 17A-20B) having balls for being received in the sockets to formball and socket joints can be attached to the base on the firstplacement guide mounting surface 607.

The offset member 705 has a first and a second end 707 and 709. Thefirst end of the offset member 705 is configured to contact the bonewhen the placement guide 700 is in the attached position and the base600 is in a position at which it is to be secured to the bone. Theoffset member 705 further comprises a longitudinal opening 711 and isconfigured such that a reference marker 130 (FIG. 11) fixed to the boneis adapted to extend through the longitudinal opening when the placementguide 700 is in the attached position and the base 600 is in a positionat which it is to be secured to the bone. The reference marker 130 istypically in the form of a wire installed in the bone so as to extendgenerally perpendicular to the tibial plateau and generally parallel tothe medial femoral condyle.

The placement guide 700 may be designed to be attachable to the base 600in only one attached position. For example, the placement guide 700 maybe shaped so that it fits between arms 611 extending from the firstplacement guide mounting surface 607 that prevent rotation of theplacement guide relative to the base 600.

The placement guide 700 further comprises an elongate member 713 havinga proximal guide hole (not shown) similar to the proximal guide hole 310discussed in connection with the embodiment shown in FIGS. 9A-11. Theelongate member 713 extends from the guide 700 in a direction towards anopposite bone of the joint and is thus configured for facilitatingorientation of the base on the bone when the placement guide 700 is inthe attached position and the base 600 is in a position at which it isto be secured to the bone.

The placement guide 700 further includes a locking arm 715 adapted toengage with the base 600 for locking the placement guide in the attachedposition. The locking arm 715 extends from the main body 717 of theplacement guide 700 in an opposite direction relative to the secondplacement guide mounting surface 701 from the direction of the locationof the offset member 705. The locking arm 715 extends around anengagement portion 613 of the base 600 and, while in this lockingposition, prevents removal of the placement guide 700 from the base. Thelocking arms 715 is flexible or breakable so that it can be moved fromlocking position and removal of the placement guide 700 from the base600 is possible. A removable pin 800 (shown by itself in FIG. 16)engages the locking arm 715 to prevent unlocking of the placement guide700 from the attached position and extends through openings 719 and 721in the locking arm and the second connector component 703 and through anopening 615 in the engagement portion 613 of the base.

The system 900 is used to position the base 600 for an implant at ajoint by inserting a first reference marker 130 into a first bone of thejoint so that one end of the first reference marker is inserted into thebone and the other end of the first reference marker is free. The system900 in the form of a preassembled combination of a base 600 and aplacement guide 700 is positioned on the bone of the joint so that thefirst reference marker 130 extends through the longitudinal opening 711in the offset 705, which functions as a first guide hole. A secondelongated reference marker such as a wire (not shown) is extendedthrough the proximal guide hole in the elongate member 713 and into thebone of the joint while orienting the system 900 comprising the base 600and placement guide 700 combination, together with the second referencemarker, so that, when the second reference marker is inserted into thebone, the second reference marker extends in a predetermined relation tothe first bone and a second bone of the joint. As described inconnection with the attachment of the base 52 in FIG. 11, the secondreference marker may be a guide wire that extends generallyperpendicular to the tibial plateau and generally parallel to the medialfemoral condyle. After securing the base 600 to the bone via bone screwsthrough bone screw holes 617, the placement guide 700 is detached fromthe base 600 by removing the pin 800 and moving the locking arm 715 fromthe locking position to an unlocked position.

The various embodiments described above are provided by way ofillustration only and should not be construed to limit the claimedinvention. Those skilled in the art will readily recognize variousmodifications and changes that may be made to the claimed inventionwithout following the example embodiments and applications illustratedand described herein, and without departing from the true spirit andscope of the claimed invention, which is set forth in the followingclaims. In that regard, various features from certain of the disclosedembodiments can be incorporated into other of the disclosed embodimentsto provide desired structure.

We claim:
 1. A method of implanting a device at a joint comprising:inserting a first reference marker into a first bone of the joint;inserting a second reference marker into a second bone of the joint;connecting the first and second reference markers to a verificationtool; moving the joint through a predetermined range of motion andutilizing the verification tool to determine whether the first andsecond reference markers move in a desired kinematic pattern withrespect to one another throughout the predetermined range of motion;aligning the first and second bones and placing an alignment guideacross the joint; using the alignment guide to properly position thedevice; relocating one of the reference markers if the desired kinematicpattern is not achieved; and implanting the device across the joint. 2.The method of claim 1, wherein the device is an joint unloading device.3. The method of claim 1, wherein the first and second reference markersare temporary markers which are removed when the device is implanted. 4.The method of claim 1, wherein the desired kinematic pattern includesmotion of the first and second reference markers away from one anotheras the joint is moved through the predetermined range of motion fromextension to flexion.
 5. The method of claim 3, wherein joint is a kneejoint and further comprising aligning an indicator rod of the alignmentguide to be parallel with a tibia and inserting reference markersthrough the alignment guide.
 6. The method of claim 1, wherein the firstand second markers comprise elongated members having an end configuredfor inserting into bone and a free end, and wherein the verificationtool has openings for receiving the free ends of the elongated members.7. The method of claim 1, wherein the verification tool includes anindicator which indicates whether the first and second reference markersmove in a desired kinematic pattern.
 8. The method of claim 5, whereinthe second marker is inserted into the second bone through the openingin the verification tool.
 9. The method of claim 1, wherein theverification tool is configured to measure a distance between the firstand second reference markers while the joint is moved through thepredetermined range of motion.
 10. The method of claim 1, wherein thefirst and second markers are K-wires and are inserted alongsubstantially parallel paths.
 11. The method of claim 1, wherein thejoint is a knee and the first marker is positioned on a femur relativeto a midpoint of Blumensaat's line.
 12. A verification tool forverification of a location for implantation of an extra-articular jointunloading device at a joint, the tool comprising: a tool body; a firstconnection member on the tool body, the first connection memberconfigured to be snapped on a first reference marker located in a firstbone; a second connection member on the tool body, the second connectionmember configured to be snapped on a second reference marker located ina second bone, wherein the first and second connection members arelongitudinally movable and rotatable with respect to each other; and anindicator configured to provide a user with information about thelocation of at least one of the first and second reference markers asthe joint is articulated.
 13. The tool of claim 12, wherein theindicator configured to determine whether the first and second referencemarkers move in a desired kinematic pattern.
 14. The tool of claim 13,wherein the indicator is a visual indicator.
 15. The tool of claim 13,wherein the indicator provides information concerning whether themarkers are moving toward and away from each other.
 16. An alignmentguide for placing an joint unloading device at a knee joint comprising:a body configured to receive a plurality of reference markers insertedin bones on either side of the knee joint; and an indicator rodextending longitudinally from the body, wherein the indicator rod isconfigured to be aligned with an axis of a tibia when the knee joint isplaced in extension.
 17. The system of claim 16, wherein the bodyincludes three tubes for receiving the reference markers.
 18. The systemof claim 17, wherein the tubes are each arranged perpendicular to thebody.
 19. The system of claim 17, wherein the tubes are perpendicular tothe indicator rod.
 20. A tool for selecting one base from among aplurality of bases having different base geometries for an implant at ajoint, comprising: a trial base having a bone contacting surface shapegenerally corresponding to a bone contacting surface shape of theplurality of bases from which the one base is to be selected; a pointerrotatably connected to the trial base; and an indicia and indicator armportion rotatably connected to the trial base, wherein, when the trialbase is positioned on a bone of the joint, the pointer is disposed in aposition relative to the indicia that indicates a desired base contourto be selected.
 21. The tool of claim 20, wherein the tool is configuredto be placed over a femoral reference marker.
 22. The tool of claim 20,wherein the indicia includes 40°, 45° and 50° markings.
 23. The tool ofclaim 20, wherein the indicator arm is configured to be directed towarda tibial reference marker.
 24. A system for selecting one base fromamong a plurality of bases having different base geometries for animplantable joint unloading system, comprising: an alignment guidecomprising a body having at least one opening for receiving a firstreference marker positioned in a femur and at least one opening forinserting a second reference marker into a tibia, and an indicator rodextending from the body, wherein the indicator rod is configured to bealigned with an axis of tibia when the knee joint is placed inextension; and a trial base having at least one opening configured to bereceived over the first reference marker, a pointer movably connected tothe trial base, and an indicia and indicator arm portion rotatablyconnected to the trial base, wherein, when the trial base is positionedon a bone of the joint, the pointer is disposed in a position relativeto the indicia that indicates a desired base to be selected.
 25. Thesystem of claim 24, wherein the pointer is rotatably connected to thetrial base.
 26. The system of claim 25, wherein the pointer is rotatablein at least dimensions with respect to the trial base.
 27. The system ofclaim 24, wherein the trial base has a bone contacting surface shaped togenerally corresponding to a bone contacting surface shape of theplurality of bases from which the one base is to be selected.
 28. Thesystem of claim 24, wherein the alignment guide body includes at leasttwo tubes for receiving the first and second reference markers.
 29. Thesystem of claim 28, wherein the at least two tubes are arranged tocontact the bone such that the alignment guide body is positionedoutside of a patient with the at least two tubes entering into one ormore incisions.
 30. A method for selecting one base from among aplurality of bases having different base geometries for an implantablejoint unloading system, comprising: inserting a first reference markerin the femur; connecting an alignment guide to the first referencemarker with an indicator rod extending from the alignment guide alignedwith an axis of tibia when the knee joint is placed in extension;inserting a second reference marker through an opening in the alignmentguide and into the tibia; and positioning a trial base over the firstreference marker, rotating the trial base until an arm of the trial basepoints to the second reference marker, and selecting a desired base tobe implanted based on an indicia shown on the trial base.
 31. The methodof claim 30, wherein a pointer on the trial base is rotatably connectedto the trial base and points to the indicia.
 32. The method of claim 31,wherein the pointer is rotatable in at least dimensions with respect tothe trial base.
 33. The method of claim 30, wherein the trial base has abone contacting surface shaped to generally corresponding to a bonecontacting surface shape of the plurality of bases from which the onebase is to be selected.
 34. The method of claim 30, wherein thealignment guide body includes at least two tubes for receiving the firstand second reference markers.
 35. The system of claim 34, wherein the atleast two tubes are arranged to contact the bone such that the alignmentguide body is positioned outside of a patient with the at least twotubes entering into one or more incisions in the patient to contact thebone.